The present invention relates to the field of read/write head positioning, and more particularly, to arrangements for moving a read/write head by a head positioner in a manner that absorbs errors from a prime mover system.
Recently, the demand for magnetic storage densities has increased from merely a few gigabytes to several hundred gigabytes. Magnetic tape systems are still among the most economical means of data storage. Tape storage systems having only a few gigabytes capacity have limited track densities and bit densities. During the write-read function, the head positioner of the tape storage system locates the head at the necessary track center line. The write-read process continues without making any further adjustment, even if there is an occurrence of an offset between the head gap and the track""s center line. In such drives, there is an arrangement to precisely locate the head at the track""s center line at the beginning of the tape, but once the write-read process begins, there is no correction performed if an offset is subsequently created between the head and the track center line.
In order to increase storage capacities to several hundred gigabytes, the track densities (defined as the number of tracks per inch) need to be increased substantially. As the track density increases, the track pitch and the track width decrease. For proper write-read operation, the magnetic head must stay at or very close to the center line of the track. Due to the narrow track pitch, this task of maintaining the head gap to the track center line is very difficult for conventional positioners. Thus, because of the narrower track pitch, the head positioner must improve in order to minimize the offset between the head and the center line of the track. In addition to increasing the track density, increasing the tape width is an alternative that increases the storage capacity. An LTO (xe2x80x9cLinear Tape Openxe2x80x9d format) cartridge is one of the examples of a data cartridge in which the track density as well as the tape width are increased in order to achieve a several hundred gigabyte capacity.
In order to meet the challenge of higher track densities and increased tape width, modern tape transports employ a combination of a coarse/fine head positioner. The coarse positioner moves the head approximately to the region of the data track to be written or read, and the fine positioner moves the head at the center line of the track with the necessary precision. As tape width increases, the access time to move the head from one track location to another track location becomes an issue. This requires a coarse positioning mechanism to provide a higher translational velocity.
Coarse positioner design generally comprises three main elements. These elements are the prime mover system, the guidance system, and an anti-rotation system. The function of the prime mover system is to translate the head positioner mass up or down with a required velocity. The guidance system ensures that during the translation, the head orientation with respect to the tape path of the tape transporter is kept within required tolerance limits. The anti-rotation system prevents the head positioner from rotating against the torque produced by the prime mover in forward or reverse direction.
In certain conventional arrangements, the prime mover system has two main elements; a lead screw and a nut. As the lead screw rotates, the nut is moved. The lead screw is supported at two ball bearings. In spite of the considerable efforts to produce a perfect lead screw, there are always anomalies in such a lead screw. For example, the lead screw has so-called radial and axial run-outs. The lead screw motion therefore has errors from the run-outs and misalignments of the ball bearings. Additionally, the threads on the nut would exhibit similar anomalies.
The nut used in conventional systems, moves the total positioner mass, and must couple to the head positioner mass such that the positioner translates per the specifications of the guidance system without introducing any errors from the prime mover system. More specifically, the nut must allow the total positioner mass to translate without adding any interference from the anomalies of the prime mover system. To address the issue of the anomalies of the prime mover system, the coarse positioning system should be designed to separate the functions of translating, and to provide guidance accuracy as the head translates. However, prior conventional designs utilizing the lead screw and floating nut type arrangement have failed to adequately address these concerns.
There is a need for a head positioning arrangement that provides proper isolation of the guidance system from the errors of the prime mover system while allowing the head positioner to be moved with a desired velocity.
This and other needs are met by embodiments of the present invention which provide a head positioner arrangement for a tape drive comprising a head positioner with a guidance system and a prime mover system, and means for isolating the guidance system from the prime mover system.
The earlier stated need is also met by another embodiment of the present invention that provides a head positioning arrangement for a tape drive, comprising a head positioner with a guidance system and a prime mover system, and a floating nut positioned between the prime mover system and the guidance system. The three-point feature of the floating nut is the only interface between the prime mover system and the guidance system. The three-point contact absorbs errors from the prime mover system and prevents the errors from interfering with guidance system.
The earlier stated needs are met by other embodiments of the present invention, which provide a head positioning arrangement comprising a base, a coarse positioning bracket movably mounted on the base, and a prime mover system coupled to the base for controllably moving the coarse positioning bracket relative to the base. A guidance system is coupled between the base and the coarse positioning bracket for guiding the coarse positioning bracket linearly during moving of the coarse positioning bracket by the prime mover system. A floating nut is coupled to the prime mover system and bears against the coarse positioning bracket. The floating nut has a three-point contact with the coarse positioning bracket. The coarse positioning bracket is biased against the floating nut to move in a first direction upon movement of the floating nut in the first direction by the prime mover system, and to move in a second direction against the biasing upon movement of the floating nut in the second direction by the prime mover system. The three-point contact remains in contact with the coarse positioning bracket throughout movement of the coarse positioning bracket in the first and second directions.
The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.